Motion facilitating tibial components for a knee prosthesis

ABSTRACT

An orthopaedic tibial prosthesis includes a tibial baseplate sized and shaped to cover substantially all of a resected proximal tibial surface, and a tibial bearing component sized to leave a posteromedial portion of the tibial baseplate exposed when the tibial bearing component is mounted to the baseplate. The exposed posteromedial portion of the tibial baseplate includes a chamfered profile which cooperates with a correspondingly chamfered profile at a posteromedial edge of the tibial bearing component to create a substantially continuous chamfer extending from the resected tibial surface to the medial articular surface of the tibial bearing component. Advantageously, this chamfer leaves an absence of material (i.e., a relief or void) at the posteromedial edge of the tibial prosthesis, thereby enabling deep flexion of the prosthesis without impingement between the tibial prosthesis and adjacent anatomic tissues or prosthetic structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/034,963, filed on Sep. 24, 2013, which application is a continuationof U.S. patent application Ser. No. 13/229,103, filed on Sep. 9, 2011,which claims the benefit under Title 35, U.S.C. §119(e) of U.S.Provisional Application Ser. No. 61/381,800, filed on Sep. 10, 2010 andentitled TIBIAL PROSTHESIS FACILITATING ROTATIONAL ALIGNMENT, the entiredisclosure of each are hereby expressly incorporated by referenceherein.

BACKGROUND 1. Technical Field

The present disclosure relates to orthopaedic prostheses and,specifically, to tibial components in a knee prosthesis.

2. Description of the Related Art

Orthopaedic prostheses are commonly utilized to repair and/or replacedamaged bone and tissue in the human body. For example, a kneeprosthesis used in total knee arthroplasty may include a tibialbaseplate that is affixed to a resected or natural proximal tibia, afemoral component attached to a resected or natural distal femur, and atibial bearing component coupled with the tibial baseplate and disposedbetween the tibial baseplate and femoral component. Knee prosthesesfrequently seek to provide articulation similar to a natural, anatomicalarticulation of a knee joint, including providing a wide range offlexion.

The tibial bearing component, sometimes also referred to as a tibialinsert or meniscal component, is used to provide an appropriate level ofconstraint and conformity at the interface between the femoral componentand the tibial bearing component. For a knee prosthesis to provide asufficient range of flexion with a desirable kinematic motion profile,the tibial bearing component and tibial baseplate must be sized andoriented to interact appropriately with the femoral component of theknee prosthesis throughout the flexion range. Substantial design effortshave focused on providing a range of prosthesis component sizes andshapes to accommodate the natural variability in bone sizes and shapesin patients with orthopaedic prostheses, while preserving flexion rangeand desired kinematic motion profile.

In addition to facilitating implantation and providing enhancedkinematics through manipulation of the size and/or geometry ofprosthesis components, protection and/or preservation of soft tissues inthe natural knee joint is also desirable.

A given prosthetic component design (i.e., a tibial baseplate, tibialbearing component, or femoral component) may be provided to a surgeon asa kit including a variety of different sizes, so that the surgeon maychoose an appropriate size intraoperatively and/or on the basis ofpre-surgery planning. An individual component may be selected from thekit based upon the surgeon's assessment of fit and kinematics, i.e., howclosely the component matches the natural contours of a patient's boneand how smoothly the assembled knee joint prosthesis functions inconjunction with adjacent soft tissues and other anatomical structures.Soft tissue considerations include proper ligament tension andminimization of soft tissue impingement upon prosthetic surfaces, forexample.

In addition to prosthetic sizing, the orientation of a prostheticcomponent on a resected or natural surface of a bone also impactssurgical outcomes. For example, the rotational orientation of a tibialbaseplate and tibial bearing component with respect to a resectedproximal tibia will affect the interaction between the correspondingfemoral prosthesis and the tibial bearing component. Thus, substantialdesign efforts have been focused on providing prosthetic componentswhich are appropriately sized for a variety of patient bone sizes andare adapted to be implanted in a particular, proper orientation toachieve desired prosthesis performance characteristics.

SUMMARY

The present disclosure provides an orthopaedic tibial prosthesisincluding a tibial baseplate sized and shaped to cover substantially allof a resected proximal tibial surface, and a tibial bearing componentsized to leave a posteromedial portion of the tibial baseplate exposedwhen the tibial bearing component is mounted to the baseplate. Theexposed posteromedial portion of the tibial baseplate includes achamfered profile which cooperates with a correspondingly chamferedprofile at a posteromedial edge of the tibial bearing component tocreate a substantially continuous chamfer extending from the resectedtibial surface to the medial articular surface of the tibial bearingcomponent. Advantageously, this chamfer leaves an absence of material(i.e., a relief or void) at the posteromedial edge of the tibialprosthesis, thereby enabling deep flexion of the prosthesis withoutimpingement between the tibial prosthesis and adjacent anatomic tissuesor prosthetic structures.

To facilitate selection of proper prosthesis components, a set of trialtibial baseplate components are provided, with each component in the setsized to substantially cover various sizes of a proximal tibial surfaceexposed after resection. Each trial component has a perimeter that issubstantially identical to the perimeter of correspondingly sized tibialbaseplate, and is therefore larger than the corresponding tibial bearingcomponent at the posteromedial portion owing to the void created by theposteromedial chamfer. The trial components include visual indicators ofthis posteromedial void, thereby establishing a visual acuity betweenthe trial components and the final assembled tibial prosthesis. Thisvisual acuity promotes surgeon confidence that the trial components areappropriately paired with their smaller counterpart permanent tibialbearing components.

In an alternative embodiment, the permanent tibial baseplate may besymmetrical or otherwise differently-shaped from the trial component.The asymmetric trial component may still be used to determine properrotation, sizing, and orientation of the permanent component, as above,but may then be replaced with the differently-shaped tibial baseplatefor final implantation. Where such a differently-shaped tibial baseplateis used, the trial component may include visual indication of thedisparity between the trial periphery and the baseplate periphery. Thisvisual indication of disparity promotes surgeon confidence in the finalimplanted position and orientation of the baseplate.

Proper rotational orientation of the baseplate and tibial bearingcomponents is assessed by comparing one or more of the trial componentsto the natural resected tibial surface. To ensure that this rotationalorientation is properly transferred to the permanent components, thetrial components provide drill guide holes which can be used to locateand orient the proper location for one or more mounting holes for thepermanent tibial baseplate. The corresponding tibial baseplate is thenprovided with fixation pegs formed at the same location relative to thebaseplate periphery. Alternatively, the provisional component mayinclude a central aperture corresponding to a stem or keel formed on thetibial baseplate.

In one form thereof, the present invention provides a tibial bearingcomponent comprising: an inferior surface; an opposing superior surfacedefining a lateral articular surface and a medial articular surface; ananteroposterior axis disposed between the lateral articular surface andthe medial articular surface and extending from an anterior edge to aposterior edge of the tibial bearing component; and a peripheral wallextending from the inferior surface to the superior surface, theperipheral wall having a tibial bearing chamfer extending from aposterior medial edge of the superior surface toward the inferiorsurface, the tibial bearing chamfer extending across at least 25% of anavailable proximal/distal distance between the superior and inferiorsurfaces at the posterior medial edge, the tibial bearing chamferforming an acute bearing chamfer angle with the inferior surface suchthat the bearing chamfer extends proximally and anteriorly from theinferior surface toward the superior surface.

In another form thereof, the present invention provides a tibialprosthesis kit, the kit comprising: a tibial baseplate including medialand lateral compartments bounded by a baseplate periphery, the medialcompartment including a posteromedial baseplate portion defining abaseplate chamfer, the baseplate chamfer defining an acute baseplatechamfer angle with respect to a coronal plane; a first tibial bearingcomponent comprising: a first inferior surface sized to fit within thebaseplate periphery; an opposing first superior surface; a first medialportion having a first medial articular surface forming part of thefirst superior surface; a first lateral portion disposed opposite thefirst medial portion with respect to an anteroposterior axis, the firstlateral portion having a first lateral articular surface forming anotherpart of the first superior surface; and a first bearing chamferextending from a posterior medial edge of the first superior surfacetoward the first inferior surface, the first bearing chamfer extendingacross at least 25% of a first available proximal/distal distancebetween the first superior and first inferior surfaces at the posteriormedial edge, the first bearing chamfer defining an acute first bearingangle with respect to the first inferior surface; and a second tibialbearing component comprising: a second inferior surface sized to fitwithin the baseplate periphery; an opposing second superior surfacedefining a second lateral articular surface and a second medialarticular surface; and a second medial portion having a second medialarticular surface forming part of the second superior surface; a secondlateral portion disposed opposite the second medial portion with respectto an anteroposterior axis, the second lateral portion having a secondlateral articular surface forming another part of the second superiorsurface; and a second bearing chamfer extending from a posterior medialedge of the second superior surface toward the second inferior surface,the second bearing chamfer extending across at least 25% of a secondavailable proximal/distal distance between the second superior andsecond inferior surfaces at the posterior medial edge, the secondbearing chamfer defining an acute second bearing angle with respect tothe second inferior surface, the second bearing component differentlysized from the first bearing component.

In yet another form thereof, the present invention provides a method ofdetermining a tibial prosthesis size, the method comprising: providing atrial component having a void indicator; placing the trial component ona resected proximal tibial surface to create a buffer zone on all sidesbetween a perimeter of the tibial surface and a perimeter of the trialcomponent, the void indicator occupying a posteromedial area of thetibial surface when the trial component is placed on the tibial surface;removing the trial component; providing a tibial baseplate having aposteromedial baseplate chamfer, and implanting the tibial baseplate onthe resected proximal tibia so that the baseplate chamfer occupies theposteromedial area.

In one aspect, the method further includes: providing a tibial bearingcomponent having a posteromedial tibial bearing chamfer; and mountingthe tibial bearing component on the tibial baseplate so that the tibialbearing chamfer and the baseplate chamfer form a substantiallycontinuous chamfer.

In another aspect, the relief created by the chamfer preventsimpingement of a femoral component, femur or soft tissues upon thetibial base plate chamfer in a deep flexion orientation corresponding toat least 155 degrees of flexion.

In still another form thereof, the present invention provides a familyof tibial prostheses, the prostheses comprising: a plurality of trialcomponents, each of the trial components comprising: a different sizeand geometrical arrangement defining a trial component perimeter, thegeometrical arrangement including asymmetry about an anteroposterioraxis; and a posteromedial area having a void indicator; a plurality oftibial baseplates having a bone-contacting surface and a superiorsurface, each of the bone-contacting surfaces defining a baseplateperimeter that is substantially identical to a respective one of thetrial component perimeters; and a plurality of tibial bearingcomponents, each of the tibial bearing components having a tibialbearing component perimeter that is substantially identical to arespective one of the trial components perimeters excluding theposteromedial area.

In one aspect, the anteroposterior axis is a home axis, the home axisdefined as a line extending from a posterior point at the geometriccenter of an attachment area between a posterior cruciate ligament andthe tibia, to an anterior point disposed on an anterior tubercle of thetibia, the tubercle having a tubercle width W, the anterior pointdisposed on the tubercle at a location medially spaced from a peak ofthe tubercle by an amount equal to W/6.

In another aspect, the void indicator comprises one of a contrastingcolor, contrasting texture, contrasting surface finish, and a geometricdiscrepancy.

In still another form thereof, the present invention provides a tibialprosthesis kit, the kit comprising: a tibial baseplate including abaseplate posteromedial portion with a baseplate chamfer formed thereon;a tibial bearing component including a tibial bearing posteromedialportion with a tibial bearing chamfer formed thereon, the tibial bearingcomponent adapted to mount to the tibial baseplate to form a tibialprosthesis, the baseplate chamfer and the tibial bearing chamfercooperating to define a gap between a posteromedial periphery the tibialbaseplate and a corresponding posteromedial periphery the tibial bearingcomponent when the tibial bearing component is attached to the tibialbaseplate; and a plurality of trial components having means foridentifying the gap.

In one aspect, the means for identifying the gap comprises one of acontrasting color, contrasting texture, contrasting surface finish, anda geometric discrepancy.

In still another form thereof, the present invention provides a tibialprosthesis kit, the kit comprising: a tibial baseplate defining abaseplate periphery, said tibial baseplate having a means for fixationto a bone; a trial component defining an asymmetric periphery differentfrom said baseplate periphery, said trial component having at least onelocator hole corresponding to the location of the means for fixation,said trial component having a void indicator indicating the location ofportions of said asymmetric periphery not present in said baseplateperiphery.

In still another form thereof, the present inventor provides a method ofdetermining a tibial prosthesis size, the method comprising: providing atrial component defining a trial component periphery and having a voidindicator within the trial component periphery; placing the trialcomponent on a resected proximal tibial surface such that the voidindicator occupies an area of the tibial surface when the trialcomponent is placed on the tibial surface; removing the trial component;providing a tibial baseplate having a baseplate periphery that isdifferent from said trial component periphery; and implanting the tibialbaseplate on the resected proximal tibia so that the baseplate peripheryoccupies an area on the proximal tibia that corresponds to the trialcomponent periphery with the void indicator removed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1A is an exploded, perspective view of a tibial baseplate andtibial bearing component in accordance with the present disclosure;

FIG. 1B is a perspective view of the tibial baseplate and tibial bearingcomponent shown in FIG. 1A;

FIG. 2A is a top plan view of a resected proximal tibial surface, with aprosthetic tibial baseplate component and tibial bearing component ofFIGS. 1A and 1B mounted thereon;

FIG. 2B is a schematic view of a periphery of the tibial baseplatecomponent shown in FIG. 2A;

FIG. 3A is a sagittal elevation, section view of one embodiment of thetibial prosthesis shown in FIG. 2A, taken along line 3A-3A;

FIG. 3B is an enlarged, partial view of the tibial prosthesis shown inFIG. 3A, illustrating a posteromedial chamfer;

FIG. 3C is a coronal elevation, section view of another embodiment ofthe tibial prosthesis shown in FIG. 2A, taken along line 3C-3C;

FIG. 3D is an enlarged, partial view of the tibial prosthesis shown inFIG. 3C, illustrating a medial transition from an articular surface to abearing periphery;

FIG. 4A is a sagittal elevation, section view of another embodiment ofthe tibial prosthesis shown in FIG. 2A, taken along line 4A-4A:

FIG. 4B is an enlarged, partial view of the tibial prosthesis shown inFIG. 4A, illustrating a posteromedial chamfer;

FIG. 5 is a top plan view of the resected proximal tibial surface shownin FIG. 2A, with a properly sized tibial trial component thereon;

FIG. 6 is a side, elevation view of the tibia and trial component shownin FIG. 2; and

FIG. 7 is a side, elevation view of the tibia and prosthetic componentsshown in FIG. 4.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate exemplary embodiments of the invention, and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION

The present disclosure provides a knee joint prosthesis which permits awide range of flexion motion, promotes desired prosthesis kinematics,protects natural soft tissue proximate the knee joint prosthesis, andfacilitates proper rotational and spatial orientation and coverage of atibial baseplate and tibial bearing component upon a resected proximaltibia.

As used herein, “proximal” refers to a direction generally toward thetorso of a patient, and “distal” refers to the opposite direction ofproximal, i.e., away from the torso of the patient. As used herein,“anterior” refers to a direction generally toward the front of apatient. “Posterior” refers to the opposite direction of anterior, i.e.,toward the back of the patient.

For purposes of the present disclosure, a sagittal plane is a planewhich extends distally and proximally, as well as anteriorly andposteriorly. For example, the plane of left/right symmetry in the humanbody is a sagittal plane. In the context of a prosthesis, such asprosthesis 10 described below, the plane that generally divides theprosthesis into medial and lateral halves is a sagittal plane, and maybe inclusive of an anteroposterior axis such as home axis A_(H)(described below).

For purposes of the present disclosure, a transverse plane isperpendicular to the sagittal plane, and extends medially and laterallyas well as anteriorly and posteriorly. For example, a plane thatseparates the human torso from the legs is a transverse plane. In thecontext of a prosthesis, the bone-contacting surface (e.g., surface 35shown in FIG. 1A and described below) and the corresponding proximalsurface of a tibia after resection both define generally transverseplanes. A coronal plane is perpendicular to the sagittal and transverseplanes. For example, the plane separating the front and back sides of ahuman is a coronal plane.

Referring to FIG. 2A, tibia T includes tibial tubercle B havingmediolateral width W, with tubercle midpoint P_(T) located on tubercle Bapproximately halfway across width W. While tubercle B is shown ashaving midpoint P_(T) at the “peak” or point of maximum anterioreminence, it is recognized that midpoint P_(T) of tibia T may be spacedfrom such a peak. Tibia T also includes attachment point C_(P)representing the geometric center of the attachment area between theanatomic posterior cruciate ligament (PCL) and tibia T. Recognizing thatthe PCL typically attaches to a tibia in two ligament “bundles,” one ofwhich is relatively anterior, lateral and proximal and the other ofwhich is relatively posterior, medial and distal, attachment point C_(P)is contemplated as representing the anterior/lateral attachment area inan exemplary embodiment. However, it is contemplated that theposterior/medial attachment area, or the entire attachment area, couldbe used.

In the context of patient anatomy, “home axis” A_(H) (FIG. 2A) refers toa generally anteroposterior axis extending from posterior point C_(P) toan anterior point C_(A), in which anterior point C_(A) is disposed ontubercle B and medially spaced from tubercle midpoint P_(T) by an amountequal to W/6. Stated another way, anterior point C_(A) is laterallyspaced by an amount equal to W/3 from the medial end of mediolateralwidth W, such that point C_(A) lies on the “medial third” of theanterior tibial tubercle.

In the context of a prosthesis, such as tibial prosthesis 10 describedbelow, “home axis” A_(H) refers to an axis oriented with respect tobaseplate 12 such that the baseplate home axis A_(H) of baseplate 12 isaligned with home axis A_(H) of tibia T after implantation of baseplate12 in a proper rotational and spatial orientation. In the illustrativeembodiment shown in FIG. 2B and described in detail below, home axisA_(H) bisects PCL cutout 28 at the posterior portion of periphery 200 oftibial plate 18 (FIG. 2A), and bisects anterior edge 202 at the anterioredge of periphery 200 of tibial plate 18. It is contemplated that homeaxis A_(H) may be oriented to other baseplate features, it beingunderstood home axis A_(H) of baseplate 12 is positioned such that thatproper alignment and orientation of baseplate 12 upon tibia T positionshome axis A_(H) of baseplate 12 coincident with home axis A_(H) of tibiaT. Home axis A_(H) of tibial baseplate 12 may be said to be ananteroposterior axis, as home axis A_(H1) extends generally anteriorlyand posteriorly when baseplate 12 is implanted upon tibia T.

The embodiments shown and described in the Figures illustrate a leftknee and associated features of a left-knee prosthesis. In an exemplaryembodiment, an associated right knee configuration is a mirror image ofthe left-knee configuration about a sagittal plane. Thus, it will beappreciated that all aspects of the prosthesis described herein areequally applicable to a left- or right-knee prosthesis.

1. Tibial Prosthesis Construction.

Referring now to FIGS. 1A and 1B, tibial prosthesis 10 includes tibialbaseplate 12 and tibial bearing component 14. Tibial baseplate 12 mayinclude a stem or keel 16 (see, e.g., FIGS. 3A, 3C and 4A) extendingdistally from a proximal tibial plate 18 for fixation of tibialbaseplate to a tibia T. Alternatively, a plurality of fixation pegs (notshown) may be provided to affix tibial plate 18 to tibia T.

Referring now to FIGS. 1A and 2A, tibial baseplate 12 includes lateralcondylar compartment 20 and medial condylar compartment 22 which formmedial and lateral “halves” of tibial plate 18 divided by home axisA_(H) (which extends between compartments 20, 22 as shown in FIG. 2B).However, lateral and medial condylar compartments 20, 22 are dissimilarin size and shape, rendering tibial plate 18 of tibial baseplate 12asymmetrical about home axis A_(H) such that medial compartment 22actually represents more than half of the total area contained withinperiphery 200. Periphery 200 represents the outer limits, or bounds, oflateral and medial compartments 20, 22.

As shown in FIG. 2B, lateral condylar compartment 20 defines radius R₁at anterolateral corner 210, and medial condylar compartment 22 definesradius R₂ at anteromedial corner 220. Anteromedial radius R₂ issubstantially larger than anterolateral radius R₁, thereby imparting arelatively more “boxy” appearance to lateral condylar compartment 20,and a more “rounded” appearance to medial condylar compartment 22.

This asymmetry is specifically designed so that peripheral wall 25traces the perimeter of the resected proximal surface of tibia T, suchthat tibial plate 18 covers a large proportion of the resected proximaltibial surface as shown in FIG. 2A. This substantial coverage encouragesand facilitates proper rotational and spatial orientation of tibialbaseplate 12 upon tibia T, and provides a large overall profile ofbaseplate 12 which creates sufficient space for large-radius,“soft-tissue friendly” edges as described in detail below. Exemplaryasymmetric profiles for tibial baseplate 12 are described in U.S. patentapplication Ser. Nos. 13/189,336, 13/189,338 and 13/189,339, each filedon Jul. 22, 2011 and entitled ASYMMETRIC TIBIAL COMPONENTS FOR A KNEEPROSTHESIS, the entire disclosures of which are hereby expresslyincorporated by reference herein.

As best seen in FIGS. 2A and 2B, lateral condylar compartment 20 oftibial plate 18 defines overall anteroposterior extent D_(L) which isless than overall anteroposterior extent D_(M) of medial condylarcompartment 22. This disparity in anteroposterior extent arises from theadditional posterior reach of medial condylar compartment 22 as comparedto lateral condylar compartment 20. The additional posteromedialmaterial of tibial plate 18 includes chamfer 32 (FIG. 1A) formed inperipheral wall 25, which forms angle α (FIG. 7) with bone-contactingsurface 35 of tibial plate 18. As described in detail below, chamfer 32forms part of a larger posteromedial chamfer that provides a reliefspace for soft tissues and bone in deep flexion of prosthesis 10.

Turning back to FIG. 1A, tibial bearing component 14 includes lateralportion 39, medial portion 41, inferior surface 36 adapted to couple totibial baseplate 12, and superior surface 38 adapted to articulate withcondyles of a femoral component (such as femoral component 60 shown inFIG. 7 and described in detail below). Superior surface 38 includeslateral articular surface 40 in lateral portion 39 and medial articularsurface 42 in medial portion 41, with eminence 44 (FIG. 2A) disposedbetween articular surfaces 40, 42. Referring to FIG. 2A, eminence 44 isa gently elevated portion which generally corresponds in shape and sizewith a natural tibial eminence of tibia T prior to resection.

Tibial plate 18 of tibial baseplate 12 further includes a distal or bonecontacting surface 35 and an opposing proximal or superior surface 34,with superior surface 34 having raised perimeter 24 and lockingmechanism 26 formed between lateral and medial compartments 20, 22.Superior surface 34 is sized to mate with inferior surface 36 of tibialbearing component 14, such that inferior surface fits entirely withinthe periphery defined by superior surface 34 (i.e., bearing component 14does not “overhang” tibial plate 18 at any point). Raised perimeter 24and locking mechanism 26 cooperate to retain tibial bearing component 14upon tibial baseplate 12. More particularly, inferior surface 36 oftibial bearing component 14 includes peripheral recess 46 sized andpositioned to correspond with raised perimeter 24 of tibial plate 18.Inferior surface 36 may further include central recess 47 (see, e.g.,FIG. 3C) disposed between lateral and medial articular surfaces 40, 42which cooperates with locking mechanism 26 of tibial plate 18 to fixtibial bearing component 14 to tibial baseplate 12 in a desired positionand orientation. However, it is contemplated that tibial bearingcomponent 14 may be affixed to baseplate 12 by any suitable mechanism ormethod within the scope of the present disclosure, such as by adhesive,dovetail tongue/groove arrangements, snap-action mechanisms, and thelike.

Exemplary tibial baseplate and tibial bearing component lockingmechanisms are described in U.S. provisional patent application Ser.Nos. 61/367,374 and 61/367,375 filed Jul. 24, 2010, and U.S. patentapplication Ser. Nos. 13/189,324 and 13/189,328 filed Jul. 22, 2011, allentitled TIBIAL PROSTHESIS, the entire disclosures of which are herebyexpressly incorporated herein by reference.

Turning to FIG. 2B, periphery 200 of tibial plate 18 surrounds lateralcompartment 20 and medial compartment 22, each of which define aplurality of lateral and medial arcs extending between anterior edge 202and lateral and medial posterior edges 204, 206 respectively. In theillustrative embodiment of FIG. 2B, anterior edge 202, lateral posterioredge 204 and medial posterior edge 206 are substantially planar andparallel for ease of reference. However, it is contemplated that edges202, 204, 206 may take on other shapes and configurations within thescope of the present disclosure, such as angled or arcuate.

Generally speaking, a “corner” of periphery 200 may be said to be thatportion of the periphery where a transition from an anterior orposterior edge to a lateral or medial edge occurs. For example, in theillustrative embodiment of FIG. 2B, the anterior-lateral corner isprincipally occupied by anterior-lateral corner arc 210, which defines asubstantially medial-lateral tangent at the anterior end of arc 210 anda substantially anteroposterior tangent at the lateral end of arc 210.Similarly, the anterior-medial corner of periphery 200 is principallyoccupied by anterior-medial corner arc 220, which defines asubstantially medial-lateral tangent at the anterior end of arc 220 anda more anteroposterior tangent at the lateral end of arc 220.Posterior-lateral arc 214 and posterior-medial arc 224 similarly definesubstantially medial-lateral tangents at their respective posterior endsand substantially anteroposterior tangents at the lateral and medialends, respectively.

As shown in FIGS. 1B and 2A, the outer periphery of tibial bearingcomponent 14 generally corresponds with the outer periphery 200 oftibial plate 18, except for the posteromedial extent of plate 18 ascompared with tibial bearing component 14. The anterolateral “corner” oftibial bearing component 14 defines radius R₃ having a generally commoncenter with radius R₁ of baseplate 12 in a transverse plane, i.e., radiiR₁ and R₃ are substantially coincident in a plan view. Similarly, theanteromedial “corner” of tibial bearing component 14 defines radius R₄having a generally common center with radius R₂ of baseplate 12 in atransverse plane, i.e., radii R₂ and R₄ are substantially coincidentwhen in a plan view. R₃ defines a slightly smaller radial length ascompared to R₁, and R₄ defines a slightly smaller radial length ascompared to R₂, such that the anterior portion of perimeter wall 54 oftibial bearing component 14 is set back slightly from the anteriorportion of peripheral wall 25 of tibial baseplate 12. As with theabove-described comparison between radii R₁ and R₂, anteromedial radiusR₄ is substantially larger than anterolateral radius R₃.

Medial portion 41 of tibial bearing component 14 may be biasedanteriorly, such that the anterior-medial edges of tibial bearingcomponent 14 and tibial plate 18 coincide as shown in FIG. 2A. Thisanterior bias leaves baseplate chamfer 32 fully exposed at the portionof tibial plate 18 corresponding to posterior-medial corner 224 andposterior edge 206 of periphery 200 (FIG. 2B). In contrast, lateralarticular surface 40 substantially completely covers lateral compartment20 of tibial plate 18, and is generally centered with respect to lateralcompartment 20. In view of this anterior bias of medial portion 41, itmay be said that tibial bearing component 14 is asymmetrically orientedupon tibial plate 18 such that medial portion 41 appears to have beenrotated forward. In addition to ensuring exposure of baseplate chamfer32, this asymmetric mounting of tibial bearing component 14 upon tibialplate 18 ensures a desired articular interaction between tibialprosthesis 10 and femoral component 60, as described in detail below.

In the illustrated embodiment, tibial plate 18 includes cutout 28 (FIG.1A) disposed between condylar compartments 20, 22 to leave PCLattachment point C_(P) (FIG. 2A) accessible and allow the PCL to passtherethrough. Tibial bearing component 14 similarly includes cutout 30(FIG. 1A). Thus, tibial prosthesis 10 is adapted for a cruciateretaining (CR) surgical procedure, in which the posterior cruciateligament is not resected during implantation of tibial prosthesis 10.However, it is contemplated that a prosthesis in accordance with thepresent disclosure may be made for “posterior stabilized” (PS) or“ultracongruent” (UC) designs in which the posterior cruciate ligamentis resected during surgery. Thus, PCL cutouts 28, 30 may be optionallyomitted for prostheses which do not retain the anatomic PCL. Oneillustrative PS design, shown in FIG. 3C, includes proximally extendingspine 45 monolithically formed with tibial bearing component 14C. Spine45 is designed to interact with a corresponding cam (not shown) of afemoral component (e.g., femoral component 60 shown in FIG. 7).

In an alternative embodiment, tibial baseplate 12 may be omitted suchthat tibial prosthesis 10 is formed solely from tibial bearing component14. Tibial bearing component 14 may have a stem or keel (not shown)similar to keel 16 of baseplate 10, or may have fixation pegs forfixation to tibia T. Tibial bearing component 14 may therefore havelateral and medial portions 39, 41 and a distal fixation structure whichare monolithically formed of a single material, such as polyethylene oranother suitable polymer. Alternatively, lateral and medial portions 39,41 may be made of a different, but integrally formed material ascompared to the distal fixation structure.

Advantageously, the relatively large area of bone contacting surface 35of tibial plate 18 facilitates a large amount of bone ingrowth wherebone ingrowth material is provided in tibial baseplate 12. For example,baseplate 12 may be at least partially coated with a highly porousbiomaterial to facilitate firm fixation thereof to tibia T. A highlyporous biomaterial is useful as a bone substitute and as cell and tissuereceptive material. A highly porous biomaterial may have a porosity aslow as 55%, 65%, or 75% or as high as 80%, 85%, or 90%. An example ofsuch a material is produced using Trabecular Metalm Technology generallyavailable from Zimmer, Inc., of Warsaw, Ind. Trabecular Metal™ is atrademark of Zimmer, Inc. Such a material may be formed from areticulated vitreous carbon foam substrate which is infiltrated andcoated with a biocompatible metal, such as tantalum, by a chemical vapordeposition (“CVD”) process in the manner disclosed in detail in U.S.Pat. No. 5,282,861 to Kaplan, the entire disclosure of which isexpressly incorporated herein by reference. In addition to tantalum,other metals such as niobium, or alloys of tantalum and niobium with oneanother or with other metals may also be used.

Generally, the porous tantalum structure includes a large plurality ofstruts (sometimes referred to as ligaments) defining open spacestherebetween, with each strut generally including a carbon core coveredby a thin film of metal such as tantalum, for example. The open spacesbetween the struts form a matrix of continuous channels having no deadends, such that growth of cancellous bone through the porous tantalumstructure is uninhibited. The porous tantalum may include up to 75%,85%, or more void space therein. Thus, porous tantalum is a lightweight,strong porous structure which is substantially uniform and consistent incomposition, and closely resembles the structure of natural cancellousbone, thereby providing a matrix into which cancellous bone may grow toprovide fixation of implant 10 to the patient's bone.

The porous tantalum structure may be made in a variety of densities inorder to selectively tailor the structure for particular applications.In particular, as discussed in the above-incorporated U.S. Pat. No.5,282,861, the porous tantalum may be fabricated to virtually anydesired porosity and pore size, and can thus be matched with thesurrounding natural bone in order to provide an improved matrix for boneingrowth and mineralization.

2. Soft Tissue Impact Reduction and Deep Flexion Enablement.

Tibial bearing component 14 advantageously reduces the potential impactof prosthesis 10 on the adjacent anatomic soft tissues of a knee afterimplantation, even when the prosthesis is articulated into deep flexionin vivo. This reduced impact results from features included in bearingcomponent 14, and such features are facilitated by the size, shape andconfiguration of tibial baseplate 12.

One feature which reduces soft tissue impact potential is baseplatechamfer 32, which cooperates with bearing chamfer 50 to create relief 52(FIG. 7). As noted above and shown in FIG. 2A, the otherwise close matchbetween peripheral wall 54 of tibial bearing 14 and peripheral wall 25of tibial baseplate 12 deviates around posteromedial corner 224 andposterior edge 206 of medial compartment 22 (see, e.g., FIGS. 2A and2B). In this shift from congruence to incongruence, medial compartment22 of tibial plate 18 extends posteriorly to cover a substantial portionof the proximal resected surface of tibia T (FIGS. 2A and 7), whilemedial portion 41 of tibial bearing component 14 only extendsposteriorly as far as the anterior end of chamfer 32. Thus, asillustrated in FIG. 7, tibial bearing component 14 does not “overhang”chamfer 32.

As best seen in FIGS. 1A and 7, baseplate chamfer 32 extends proximallyand anteriorly from a posterior/distal edge 62, corresponding toposterior edge 206 of periphery 200 shown in FIG. 2B, to ananterior/proximal edge 64 of chamfer 32. Similarly, bearing chamfer 50extends proximally and anteriorly from posterior/distal edge 66, whichis coincident with inferior surface 36 of bearing component 14, to ananterior/proximal edge 68 at the boundary of medial articular surface42. When tibial bearing component 14 is assembled to tibial baseplate 12as shown in FIGS. 1B and 7, medial portion 41 of tibial bearingcomponent 14 (described above) is positioned to substantially alignchamfers 32, 50. When so aligned, posterior/distal edge 66 of bearingchamfer 50 is disposed near anterior/proximal edge 64 of baseplatechamfer 32, such that chamfers 32, 50 cooperate to define asubstantially continuous chamfer extending from the resected surface oftibia T to medial articular surface 42. However, as noted below, it isalso contemplated that tibial and baseplate chamfers can cooperate todefine a discontinuous chamfer within the scope of the presentdisclosure

Chamfers 32, 50 cooperate to define relief 52 (FIG. 7) formed betweenfemur F and tibial plate 18 when tibial prosthesis 10 is in a deepflexion orientation. In the illustrated embodiment of FIG. 7, the deepflexion orientation is defined by angle β between anatomic tibia axisA_(T) and anatomic femoral axis A_(F) of up to about 25 degrees to about40 degrees, for example (i.e., about 140 degrees to 155 degrees offlexion or more).

Although asymmetric periphery 200 is designed to closely match ananatomic resected tibial surface as described above, certain aspects ofperiphery 200 are designed to intentionally deviate from the calculatedanatomical shape to confer particular advantages with regard tominimization of soft tissue impact and the associated implanted kneeprosthesis. Referring to FIG. 2A, for example, posterior edge 206 (FIG.2B) of medial compartment 22 may be “pulled back” from the adjacentposterior-medial edge of tibia T to define void 58. In an exemplaryembodiment, void 58 is created by leaving about 4 mm (measured as ananteroposterior extent) of the proximal resected surface of tibia Texposed. However, it is contemplated that void 58 may be smaller, or maybe nonexistent. For some patient anatomies, for example, it may bepossible to maximize tibial coverage by eliminating void 58 entirely(i.e., by positioning posterior edge 206 of medial compartment flushwith the corresponding edge of tibia T). A surgeon may choose toeliminate gap 58 when presented with the opportunity to do so, providedother portions of periphery 200 do not extend beyond the periphery ofthe resected proximal surface of tibia T.

As illustrated in FIG. 7, void 58 cooperates with chamfers 32, 50 tocreate extra space for adjacent soft tissues and bone, particularly whenprosthesis 10 is in a deep flexion configuration as illustrated.Advantageously, relief 52 between femur F and tibia T, made possible bychamfers 32, 50 as described above, cooperates with the “pulled back” orincongruent posterior medial void 58 to allow the deep flexionorientation to be achieved without allowing soft tissues to becometrapped and impinged between femoral component 60/femur F and tibialplate 18/tibial bearing component 14. In deep flexion, soft tissues inthe region of relief 52 can shift slightly into void 58 between femur Fand tibia T within minimal resistance, thereby mitigating soft-tissueimpacts by decreasing the likelihood of, e.g., compression orimpingement with surrounding components. Moreover, any contact that mayoccur between a prosthesis made in accordance with the presentdisclosure and adjacent soft tissues will occur against the flat andbroadly rounded surfaces of the prosthesis, such the impact of suchcontact on the tissue is minimized. To this end, it is contemplated thatthe specific geometry of chamfers 32, 50 may be modified for individualpatient needs, such as to accommodate abnormally positioned and/or sizedadjacent soft tissues.

In the illustrated embodiment of FIG. 7, bearing chamfer 50 defines asubstantially linear profile in a sagittal plane. Where this linearprofile extends across the medial/lateral extent of chamfers 32, 50,chamfers 32, 50 will also be generally coplanar, as illustrated.Chamfers define angle α with a transverse plane, e.g., with superiorsurface 34, bone contacting surface 35 and/or inferior surface 36 (whichall lie in a generally transverse plane in the illustrated embodiment).Angle α is an acute angle that may have a value as little as about 35degrees or 50 degrees and as large as about 55 degrees, 61 degrees, 70degrees or 75 degrees, or within any range defined by any of theforegoing values.

Lateral chamfer 51 (FIG. 1A) may also be provided in order to facilitatea smooth transition from lateral articular surface 40 to the interfacebetween inferior surface 36 of tibial bearing component 14 and superiorsurface 34 of tibial baseplate 12. Because lateral compartment 20 ofperiphery 200 (FIGS. 2A and 2B) provides maximum coverage of theresected proximal surface of tibia T, not all of the substantiallyconforming lateral portion 39 of tibial bearing 14 is needed to formlateral articular surface 40. Lateral chamfer 51 occupies the marginalspace near articular surface 40, which is not normally used inarticulation of prosthesis 10 with femoral component 60 (FIG. 7).

Advantageously, the smooth, rounded transition provided by lateralchamfer 51 provides clearance for bone and tissue during flexion. If anadjacent soft tissue does come into contact with lateral chamfer 51, thetension arising from such contact will be lower as compared to aprosthesis lacking such chamfer. Moreover, as with the other chamfersand rounded profiles provided on prosthesis 10, the rounded transitionof lateral chamfer 51 minimizes the impact caused by any contact whichmay occur between chamfer 51 and adjacent soft tissues. At the sametime, the buildup of material around lateral chamfer 51 providesposterior constraint to femoral component 60 (FIG. 7) and strengthensthe posterior portion of lateral portion 39 of bearing component 14.

It is contemplated that bearing chamfer 50 may have an arcuate profilein a sagittal, coronal and/or transverse plane, and may include convexor concave curvature as required or desired for a particularapplication. For example, bearing component 14A shown in FIG. 3A issimilar to bearing component 14 described above, and reference numbersin FIGS. 3A and 3B refer to analogous structures shown in FIGS. 1A and2A and described above with respect to bearing component 14. However,chamfer 50A defines a slight curve in a sagittal plane as chamfer 50Aextends from anterior/proximal edge 68A toward posterior/distal edge 66Aof tibial bearing component 14A. For purposes of evaluating angle α(FIG. 7) in the context of curved chamfer 50A, a sagittal tangent linedrawn at anterior/proximal edge 68A and compared to a coronal plane asdescribed above. In the exemplary illustrated embodiment, angle α isabout 61 degrees.

In the context of chamfers, e.g. chamfers 32, 50 and 50A, chamfer edgesare referred to herein as “anterior/proximal” and “posterior/distal.”These references refer to the relative positions of the chamfer edges inthe context of the chamfers themselves, in the context of the positionand orientation of the tibial prosthesis after implantation. Thus, an“anterior/proximal” edge is located at or near the anterior and proximalterminus of the chamfer, while a “posterior/proximal” edge located at ornear the posterior and distal terminus of the chamfer (i.e., at theopposite end of the chamfer).

In the illustrative embodiment of FIG. 3A, chamfer 50A spanssubstantially the entire available proximal/distal distance, i.e., fromsuperior surface 38A to anterior/proximal edge 64 of baseplate chamfer32. However, it is contemplated that a chamfer in accordance with thepresent disclosure may extend across only a part proximal/distaldistance, beginning near superior surface 38A but ending at a locationproximal of the junction between the tibial plate (e.g., plate 18) andthe tibial bearing component (e.g., component 14). After “early”terminus of the chamfer, the remainder of the vertical distance may betaken up by a vertical section of the bearing component periphery.

For example, chamfer 50A may extend as little as 25%/o or 32% of thetotal available proximal/distal distance, or as much as 100% of thetotal available proximal/distal distance, or may span and percentagedistance within any range defined by any of the foregoing values.Moreover, it is contemplated that the configuration of chamfer 50A mayvary depending on the configuration of tibial bearing component 14A.Where bearing component 14A is relatively thin, such as about 9-10 mm,for example, chamfer 50A may extend across a relatively largerproportion of the total available proximal/distal distance.

In some instances, bearing component 14A may be made thicker toaccommodate additional resection of tibia T. For example, one suchthicker bearing component is illustrated as component 14B, shown FIG. 4Aand discussed below. In these instances, a similar chamfer to chamfer50A may be provided in the proximal 9-10 mm of the availableproximal/distal distance, while the remainder of such distance may besubstantially vertical. This chamfer configuration retains theadvantages provided by chamfer 50A, such as avoidance of soft tissue andbone impingement in deep flexion. Thus, in a relatively thickercomponent, a relatively smaller proportion of the total availableproximal/distal distance may be needed to create a chamfer whichprovides the benefits described herein. In an exemplary embodiment,tibial bearing component may be provided as a kit of increasingthicknesses, with each thickness growing incrementally larger by 0.5mm-1.0 mm. It is contemplated that such incremental growth in thicknessmay be larger, such as 2 mm, 3 mm or 4 mm for example.

In some other instances, the distal bone stock of femur F (FIG. 7) issignificantly resected and tibial bearing component 14A is made thickerto accommodate the resulting proximal/distal joint space occupied byprosthesis 10. In these instances, a large proportion of the thickerbearing component may be given over to chamfer 50A, such that chamfer50A extends across a large proportion of the available proximal/distaldistance. This extensive chamfer 50A will advantageously minimize thechances for impingement of the adjacent soft tissues and bone.

The slight sagittal curve of chamfer 50A (described above) defines asagittal chamfer radius R_(C1) (FIG. 3A) which may be between as littleas 5 mm or 65 mm and as much as 75 mm or 180 mm, or may be any valuewithin any range defined by any of the foregoing values. Radius R_(C1)extends across an anteroposterior extent D_(CA) of about 2.0 mm, suchthat the length of the arc defined by radius R_(C1) is about 4 mm whereangle α is 61 degrees (as noted above). However, it is contemplated thatanteroposterior extent D_(CA) may be between about 0.5 mm and about 10.0mm, and the arc length may vary accordingly.

A second radius, shown as radius R_(C2) in FIG. 3A, is tangent to theposterior/distal end of radius R_(C1) and spans the remaining distanceto posterior/distal edge 66A to complete chamfer 50A. Radius R_(C2) issmaller than radius R_(C1), and may have a value as little as 5 mm or12.5 mm and as much as 12.8 mm or 180 mm, or may be any value within anyrange defined by any of the foregoing values. Radius R_(C1) cooperateswith radius R_(C2) to span the entire anteroposterior extent D_(CP) ofchamfer 50A, which extends from anterior/proximal edge 68A toposterior/distal edge 66A of bearing chamfer 50A as noted above.Anteroposterior extent D_(CP) ranges from about 0.5 mm to about 10.0 mm.In the illustrated exemplary embodiment of FIG. 3B, anteroposteriorextent D_(CP) is about 2.7 mm. Thus, in the illustrated embodiment, theanteroposterior extent of radius R_(C2) is about 0.7 mm.

The particular arrangement of chamfer 50A, as described above, has beenfound to represent an excellent balance between competing interests. Onone hand, soft-tissue clearance is maximized by decreasing angle α,which increases the volume available in void 58. On the other hand, theadditional material afforded by increasing angle α at the posteromedialportion of bearing component serves as a strengthening buttress, therebyproviding a more robust bearing component. Chamfer 50A represents astrong component geometry that also provides enough space for naturalsoft tissues across a wide range of expected anatomical variabilityamong patients.

However, it is contemplated that other chamfer profiles may be utilizedwithin the scope of the present disclosure. Such profiles may include,for example, multiple linear sections cooperating to approximate arounded profile, a pair of linear sections, or a concave roundedprofile. Moreover, it is contemplated that patient-specific chamferprofiles may be created to match the anatomies of individual patients.For a patient-specific design, the posteromedial chamfer may be designedto correspond to the sagittal profile of the portion of the femur whichis adjacent the posteromedial chamfer in deep flexion of the knee.

In an exemplary embodiment, a kit of prostheses may be provided withbearing components that all share common geometrical features of chamfer50A. Referring to FIG. 3A, for example, bearing component 14A definesdistance Dc from the anterior edge thereof to anterior/proximal edge 68Aof bearing chamfer 50A. In a kit of different prosthesis sizes designedto accommodate patients having various bone sizes, distance Dc may varywidely. For example, distance Dc may be as little as 20 mm, 25 mm or 36mm for small prosthesis sizes, and as much as 56 mm, 65 mm, or 75 mm forlarge prosthesis sizes, or may be any value within any range defined byany of the foregoing values.

Despite this substantial variability, exemplary bearing components(including component 14A) can utilize a common angle α, anteroposteriorextent D_(CA) of the proximal/anterior portion of the chamfer, andoverall chamfer anteroposterior extent D_(CP) as described above.However, it is contemplated that radii R_(C1), R_(C2) may vary acrossprosthesis sizes, such as within the ranges set forth above, in order toensure smooth and “soft-tissue friendly” transitions from the medialarticular surface (e.g., surface 42) to the chamfer (e.g., chamfer 50A).

Turning to FIGS. 4A and 4B, prosthesis 10B including a thickened tibialbearing component 14B is shown. Bearing component 14B shown in FIG. 4Ais similar to bearing component 14A described above, and referencenumbers in FIGS. 4A and 4B refer to analogous structures shown in FIGS.3A and 3B and described above with respect to bearing component 14A.However, bearing component 14B defines overall thickness T_(B) which issubstantially larger than the corresponding overall thickness T_(A) ofbearing component 14A. Bearing component 14B defines the same overallanteroposterior extent as bearing component 14A (i.e., distance Dc plusdistance D_(CP)), and may be used interchangeably with bearing component14A to effectively increase the overall thickness of prosthesis 10. Suchincreased thickness may be used to accommodate a more extensiveresection of tibia T, as noted above, or to accommodate the ligamentconfiguration of a particular patient, for example.

Thickened bearing component 14B includes bearing chamfer 50B, whichspans substantially the entire distance in a sagittal plane, as shown,from anterior/proximal edge 68B to posterior/distal edge 66B. Despitethis additional proximal/distal span of chamfer 50B as compared tochamfer 50A, anteroposterior extents D_(CA) and D_(CP) remain unchanged,i.e., at about 2.0 mm and about 2.7 mm respectively. Angle α, againtaken from a tangent to the arcuate sagittal profile of the proximalportion of chamfer 50B, also remains unchanged.

Radius R_(C3), which remains the radius value for chamfer 50B across theanteroposterior extent D_(CA) in a similar fashion to Radius R_(C1)discussed above, is larger than radius R_(C4) which extends across theremainder of overall anteroposterior extent D_(CP) in similar fashion toradius R_(C2). However, the nominal values of radii R_(C3), R_(C4) maybe different from radii R_(C1), R_(C2) respectively. In an exemplaryembodiment, for example, radius R_(C3) may have a value as little as 55mm or 65 mm and as much as 75 mm or 180 mm, or may be any value withinany range defined by any of the foregoing values. Radius R_(C4) may havea value as little as 5 mm or 12.5 mm and as much as 12.8 mm or 180 mm,or may be any value within any range defined by any of the foregoingvalues.

Advantageously, chamfer 50B defines a chamfer profile that issubstantially the same as chamfer 50A near anterior/proximal edge 68B,thereby preventing impingement of femur F and/or adjacent soft tissuesin a similar manner to chamfer 50A. Meanwhile, the reduction in radiusR_(C3) as compared to radius R_(C1), imparts an overall “steeper”sagittal profile to chamfer 50B as compared to chamfer 50A. This steeperprofile provides additional posterior buttressing of medial portion 41A,while the additional thickness T_(B) provides for ample volume in void58 for soft tissue clearance.

In addition to the posteromedial features discussed above, additionalsoft-tissue impact reduction may be achieved at the medial and lateraledges of bearing component 14. The relatively large size of tibial plate18 (covering a large proportion of the resected proximal surface oftibia T) cooperates with the close congruence of tibial bearingcomponent 14 thereto to enable a relatively large superior surface 38 oftibial bearing component 14. Because not all of this large superiorsurface area 38 is needed for lateral and medial articular surfaces 40,42 (FIG. 2A), tibial bearing component 14 provides sufficientnon-articular surface area around the periphery of lateral and medialarticular surfaces 40, 42 to allow for “pulled back” areas andrelatively large-radius, rounded transitions between such articularsurfaces and peripheral wall 54 of tibial bearing component 14. Thesefeatures minimize or prevent friction between tibial prosthesis 10 andany surrounding soft tissues, such as the iliotibial (IT) band, whichmay remain in place after implantation of prosthesis 10.

Similar to the “pulled back” portion of periphery 200 in theposteromedial portion at posterior-medial corner 224 and posterior edge206, described in detail above, tibial baseplate 12 and tibial bearingcomponent 14 each have anterior-lateral corners which are intentionally“pulled back” from an expected periphery of tibia T to create gap 56(FIG. 2A) between the anterior-lateral area of the resected surface oftibia T and prosthesis 10. Advantageously, gap 56 moves theanterior-lateral corners of baseplate 12 and tibial bearing component 14away from the area typically occupied by the iliotibial band, therebyminimizing the potential for impingement of the IT band upon prosthesis10. In an exemplary embodiment, gap 56 may range from 0.5 mm for asmall-size prosthesis, to 1 mm for a medium-sized prosthesis, to 2 mmfor a large-sized prosthesis.

For certain patients or in certain ranges of prosthesis articulation,however, the human iliotibial (IT) band may touch the anterolateralcorner of prosthesis 10. In some instances, the medial collateralligament (MCL) may also touch the medial edge of prosthesis 10. As notedabove, the large available surface area afforded by asymmetric periphery200 of tibial baseplate 12 also affords ample space for peripheraltransitions from superior surface 38 to peripheral wall 54 of tibialbearing component 14.

Turning to FIGS. 3C and 3D, transition radii R_(TL), R_(TM) areillustrated as the radii formed by the transition between lateral andmedial articular surfaces 40, 42 and lateral and medial edges 72, 74 ofperipheral wall 54 respectively. As best seen in FIG. 3D with respect tothe medial side of prosthesis 10C, the ample margin between the outerlimits of medial articular surface 42 and medial edge 74 of peripheralwall 54 allows medial transition radius R_(TM) to be relatively large,thereby allowing such transition to define a relatively large convexprofile at lateral edge 72 and medial edge 74 of peripheral wall 54while still leaving sufficient concave space, constraint and conformityfor articular surfaces 40, 42. Lateral transition radius R_(TL)similarly occupies a large margin between the outer limits of lateralarticular surface 40 and lateral edge 72 of peripheral wall 54, thoughthe margin is slightly smaller. Therefore, lateral transition radiusR_(TL) may be slightly less than medial transition radius R_(TM).

In an exemplary embodiment, medial transition radius R_(TM) is at leastzero mm or 0.45 mm and may be as large as 3 mm, 5 mm or 7 mm, or may beany value within any range defined by any of the foregoing values.Lateral transition radius R_(TL) is at least zero mm or 0.5 mm and maybe as large as 2 mm, 5 mm or 7 mm, or may be any value within any rangedefined by any of the foregoing values.

In addition to radii R_(TM), R_(TL) the respective transitions fromlateral and medial articular surfaces 40, 42 to lateral and medial edges72, 74 may also be expressed with reference to the arc length defined byradii R_(TM), R_(TL). Moreover, a longer arc length results in anincreasingly broad, convex lateral and medial transition, which in turnprovides a large contact area for soft tissue. For example, if anadjacent soft tissue structure (e.g., the IT band or medial collateralligament) comes into contact with tibial bearing component 14, minimalcontact pressures therebetween are experienced if large arc lengths areprovided. In an exemplary embodiment, the medial arc length may be aslittle as 0 mm or 0.83 mm and may be as large as 6.4 mm, or may be anyvalue within any range defined by any of the foregoing values. Lateralare length may be as little as zero mm or 0.9 mm and may be as large as3.5 mm or 6.4 mm, or may be any value within any range defined by any ofthe foregoing values.

Further, the anterolateral “pull back” of the anterior-lateral corner ofprosthesis 10, described above, allows the correspondinganterior-lateral corner of bearing component 14 to maintain separationfrom the IT band through a wide range of flexion, such that only verylow contact pressures are present in the limited circumstances wherecontact may occur.

Prosthesis 10C shown in FIG. 3C is similar to prostheses 10, 10A, 10Bdescribed above, and reference numbers in FIGS. 3C and 3D refer toanalogous structures shown in FIGS. 1A through 3B, 4A and 4B anddescribed above with respect to prostheses 10, 10A and 10B. Moreover, itshould be appreciated that the features described herein with respect toany of prostheses 10, 10A, 10B may be applied to each of the prosthesesdescribed herein.

For example, in the illustrative embodiment of FIG. 3C, tibial bearingcomponent 14C includes spine 45 extending proximally from superiorsurface 38 rather than eminence 44. As noted above, spine 45 isappropriate for use in a posterior-stabilized (PS) prosthesis. Largetransition radii R_(T) may be provided on PS designs as shown, or on CRdesigns.

Tibial prosthesis 10 (inclusive of tibial prostheses 10A, 10B and 10C)can be considered “soft tissue friendly” because the edges of tibialbearing component 14 and tibial plate 18, including chamfers 32, 50, aresmooth and rounded, so that soft tissue coming into contact with theseedges will be less likely to chafe or abrade. Further, the highcongruence peripheral wall 54 of bearing component 14 and peripheralwall 25 of baseplate 12 provides coverage of nearly all of superiorsurface 34 of baseplate 12 with bearing component 14, thereby preventingcontact between any soft tissue and any metal edge of baseplate 12.Instead, where contact does occur, it is with the soft, polymeric edgesof tibial bearing 14 or with the flat or gently convex surfaces ofchamfers 32, 50.

3. Trial Tibial Prostheses

As noted above, a kit of tibial prosthesis 10 may be provided with avariety of sizes and configurations to accommodate different bone sizesand geometries. The choice of one particular size may be plannedpreoperatively such as through preoperative imaging and other planningprocedures. Alternatively, an implant size may be chosen, or a previoussize choice modified, intraoperatively. To facilitate properintraoperative selection of a particular size for tibial prosthesis 10from among a range of available sizes, and to promote proper orientationof the chosen prosthesis 10, tibial prosthesis 10 may be part of a kitincluding one or more template or “trial” components.

Referring now to FIGS. 5 and 6, trial prosthesis 100 may be temporarilycoupled to tibia T for intraoperative sizing evaluation of tibialprosthesis 10 and initial steps in the implantation of tibial prosthesis10. Trial prosthesis 100 is one of a set of trial prostheses provided asa kit, with each trial prosthesis having a different size andgeometrical configuration. Each trial prosthesis in the set of trialprostheses corresponds to one among several sizes of permanentprosthesis 10, such as to varying peripheries 200 of tibial baseplate 12as described above.

For example, as shown in FIG. 5, trial prosthesis 100 defines superiorsurface 112 generally corresponding in size and shape to periphery 200of tibial plate 18, and including lateral portion 102 and medial portion104. Like periphery 200, superior surface 112 is asymmetrical about homeaxis A_(H), with lateral portion 102 having a generally shorter overallanteroposterior extent as compared to medial portion 104 (in partbecause medial portion 104 includes void indicator 106 as discussedbelow). In addition, the anterolateral “corner” of lateral portion 102defines radius R₁, which is identical to radius R₁ of periphery 200,while the anteromedial “corner” of medial portion 104 defines radius R₂,which is identical to radius R₂ of periphery 200 and is thereforegreater than radius R₁.

Moreover, trial prosthesis 100 includes perimeter wall 114 which definesa substantially identical periphery as peripheral wall 25 of tibialplate 18, and therefore has the same geometrical features and shapes ofperiphery 200 described above with respect to tibial plate 18. Thus, thenature of the asymmetry of trial prosthesis 100 changes across thevarious sizes of tibial prosthesis provided in the kit including trialprosthesis 100.

In an alternative embodiment, a trial prosthesis may be provided whichis designed to extend completely to the posterior-medial edge of thenatural tibial resection periphery. Thus, such a trial wouldsubstantially completely cover the resected tibial surface, therebyaiding in determination of a proper rotational orientation of the trial(and, therefore, of the final tibial baseplate 12). In this alternativeembodiment, the trial prosthesis lacks the posterior-medial “pull back”of tibial plate 18, described above, and therefore does not define void58.

Trial prosthesis 100 includes void indicator 106 disposed at theposterior portion of medial portion 104, which occupies a givenparticular area of superior surface 112 and peripheral wall 114corresponding to chamfer 32 of baseplate 12. Specifically, voidindicator 106 indicates that portion of baseplate 12 where chamfer 32 isleft exposed after tibial bearing component 14 attached to baseplate 12.Thus, void indicator 106 provides a visual marker for the ultimatelocation of relief 52 (discussed above) with respect to tibia T afterimplantation of tibial prosthesis 10.

Void indicator 106 advantageously facilitates proper rotational andspatial orientation of trial prosthesis 100 on the resected proximalsurface of tibia T by allowing a surgeon to visually match tibialbearing component 14 with trial prosthesis 100, as described in detailbelow. In the illustrated embodiment, void indicator 106 is an area ofvisual and/or tactile contrast with the remainder of tibial plate 18.This contrast may include, for example, a contrasting color, texture,surface finish, or the like, or may be formed by a geometric discrepancysuch as a step or lip, for example.

Referring specifically to FIG. 3, trial prosthesis 100 further includesa plurality of peg hole locators 108 corresponding to the properlocation for peg holes in tibia T to receive pegs (not shown) extendinginferiorly from tibial plate 18 of tibial baseplate 12. Advantageously,peg hole locators 108 allow a surgeon to demarcate the appropriatelocation on the resected proximal surface of tibia T for peg holecenters after the proper size and orientation for trial prosthesis 100has been found. The marked peg hole centers facilitating eventualdrilling of properly located peg holes in tibia T after trial prosthesishas been removed, as discussed in detail below. Alternatively, peg holelocators 108 may be used as drill guides to drill appropriatelypositioned peg holes while trial prosthesis 100 is still positioned ontibia T. As an alternative to peg hole locators 108, it is contemplatedthat a central aperture may be provided as a keel or stem locator fordemarcating the proper location of keel 16 (FIG. 3A).

Void indicator 106 may also be used to demarcate the implanted positionand location of a baseplate which is symmetric, or has any otherperiphery which is different from periphery 200. In some instances, forexample, it may be desirable to use a tibial baseplate different frombaseplate 12. However, the advantages conferred by the asymmetricperiphery of baseplate 12, such as proper rotational orientation andpositioning, may still be realized. Asymmetric trial prosthesis 100 maybe used to locate the proper location for peg holes or a keel, asdiscussed herein, with void indicator 106 offering a visual indicationof which part of the resected proximal surface of tibia T will not becovered over by the differently-shaped tibial baseplate. When the tibialbaseplate is implanted, it will have the same advantageousrotation/location as baseplate 12 even if the differently-shapedbaseplate covers less bone. The surgeon will also be assured that thoseareas of bone not covered by the differently-shaped prosthesis areproper, having previously seen such areas covered by void indicator 106.

4. Tibial Prosthesis Implantation

In use, a surgeon first performs a resection of tibia T usingconventional procedures and tools, as are well-known in the art.Exemplary surgical procedures and associated surgical instruments aredisclosed in “Zimmer LPS-Flex Fixed Bearing Knee, Surgical Technique,”“NEXGEN COMPLETE KNEE SOLUTION, Surgical Technique for the CR-Flex FixedBearing Knee” and “Zimmer NexGen Complete Knee SolutionExtramedullary/Intramedullary Tibial Resector, Surgical Technique”(collectively, the “Zimmer Surgical Techniques”), copies of which aresubmitted on even date herewith, the entire disclosures of which arehereby expressly incorporated by reference herein.

In an exemplary embodiment, a surgeon will resect the proximal tibia toleave a planar surface prepared for receipt of a tibial baseplate. Forexample, the surgeon may wish to perform a resection resulting in atibial slope defined by the resected tibial surface, which typicallyslopes proximally from posterior to anterior (i.e., the resected surfaceruns “uphill” from posterior to anterior). Alternatively, the surgeonmay instead opt for zero tibial slope. Varus or valgus slopes may alsobe employed, in which the resected surface slopes proximally or distallyfrom medial to lateral. The choice of a tibial and/or varus/valgusslope, and the amount or angle of such slopes, may depend upon a varietyof factors including correction of deformities, mimicry of thenative/preoperative tibial slope, and the like.

Tibial baseplate 12 is appropriate for use with a tibial slope of aslittle as zero degrees and as much as 9 degrees, and with a varus orvalgus slope of up to 3 degrees. However, it is contemplated that atibial baseplate made in accordance with the present disclosure may beused with any combination of tibial and/or varus/valgus slopes, such asby changing the angular configuration of keel 16 with respect tobone-contacting surface 35.

With a properly resected proximal tibial surface, the surgeon selectstrial prosthesis 100 from a kit of trial prostheses, with eachprosthesis in the kit having a different size and geometricalconfiguration (as discussed above). Trial prosthesis 100 is overlaid onthe resected surface of tibia T. If trial prosthesis 100 isappropriately sized, a small buffer zone 110 (FIG. 5) of exposed bone ofresected tibia T will be visible around the periphery of trialprosthesis 100. Buffer zone 110 should be large enough to allow asurgeon to rotate and/or reposition trial prosthesis 100 within a smallrange, thereby offering the surgeon some flexibility in the finalpositioning and kinematic profile of tibial prosthesis 10. However,buffer 110 should be small enough to prevent trial prosthesis 100 frombeing rotated or moved to an improper location or orientation, or frombeing implanted in such as way as to produce excessive overhang of theedge of trial prosthesis 100 past the periphery of the resected tibialsurface. In one exemplary embodiment, for example, buffer zone 110 willbe deemed to be appropriate when trial prosthesis 100 can be rotatedfrom a centered orientation by up to +/−5 degrees (i.e., in eitherdirection). In other embodiments, it is contemplated that such rotationmay be as much as +/−10 degrees or +/−15 degrees. In still otherembodiments, trial prosthesis 100 may substantially completely match theproximal resected surface of tibia T, such that buffer zone 110 iseliminated and no rotational freedom is afforded.

To aid the surgeon in finding proper rotational orientation, trialprosthesis 100 may include anterior and posterior alignment indicia 70A,70P (FIG. 5). Similarly positioned marks may be provided on tibial plate18 for reference upon final implantation thereof. The surgeon can alignanterior indicium 70A with anterior point C_(A) and posterior indicium70P with PCL attachment point C_(P), thereby ensuring the anatomical andcomponent home axes A_(H) (described above) are properly aligned.Alternatively, a surgeon may use indicia 70A, 70P to indicate a desireddeviance from alignment with home axis A_(H). As noted above, deviationof up to 5 degrees is envisioned with the exemplary embodimentsdescribed herein. A surgeon may choose to orient indicia 70A, 70P toanother tibial landmark, such as the middle of the patella or the medialend of tibial tubercle B.

The large coverage of trial prosthesis 100 (and, concomitantly, oftibial plate 18) ensures that tibial baseplate 12 will be properlypositioned and oriented on tibia T upon implantation, thereby ensuringproper kinematic interaction between tibial prosthesis 10 and femoralcomponent 60. If buffer zone 110 is either nonexistent or too large,another trial prosthesis 100 may be selected from the kit and comparedin a similar fashion. This process is repeated iteratively until thesurgeon has a proper fit, such as the fit illustrated in FIGS. 3 and 4,between trial prosthesis 100 and the proximal resected surface of tibiaT.

With the proper size for trial prosthesis 100 selected and itsorientation on tibia T settled, trial prosthesis 100 is secured to tibiaT, such as by pins, screws, temporary adhesive, or any otherconventional attachment methods. Once trial prosthesis 100 is sosecured, other trial components, such as trial femoral components andtrial tibial bearing components (not shown) may be positioned and usedto articulate the leg through a range of motion to ensure a desiredkinematic profile. During such articulation, void indicator 106 may beused to indicate to the surgeon that any impingement of femoralcomponent 60, femur F or adjacent soft tissues upon trial prosthesis 100at void indicator 106 will not occur when tibial prosthesis 10 isimplanted. Once the surgeon is satisfied with the location, orientationand kinematic profile of trial prosthesis 100, peg hole locators 108 maybe used to demarcate the appropriate location of peg holes in tibia Tfor tibial baseplate 12. Such peg holes may be drilled in tibia T withtrial prosthesis 100 attached, or trial prosthesis 100 may be removedprior to drilling the holes.

With tibia T thus prepared for receipt of tibial prosthesis 10, tibialbaseplate 12 may be provided by the surgeon (e.g., procured from a kitor surgical inventory), and implanted on tibia T, such that implant pegs(not shown) fit into holes previously identified and created using peghole locators 108 of trial prosthesis 100. Tibial baseplate 12 may beselected from a family or kit of tibial baseplate sizes to correspondwith the chosen size and/or configuration of trial component 100,thereby ensuring that tibial plate 18 will cover a large proportion ofthe resected proximal surface of tibia T, as trial prosthesis 100 didprior to removal.

In an alternative embodiment, the surgeon may provide a tibial baseplate(not shown) having a periphery that does not match periphery 200 oftrial prosthesis 100. For example, the surgeon may choose a baseplatewhich is symmetric about an anteroposterior axis. In another example, asurgeon may choose a tibial baseplate having the same periphery astibial bearing component 14, and having a vertical peripheral wall inplace of chamfer 32. In this embodiment, void indicator may beconfigured to show the non-acuity between periphery 200 and thedifferently-shaped tibial baseplate, as described above. Uponimplantation of the differently-shaped tibial baseplate, the surgeon canvisually verify that the portions of bone previously covered by voidindicator are not covered by the tibial baseplate

Tibial baseplate 12 (or an alternative baseplate, as described above) isimplanted upon the proximal surface of tibia T in accordance withaccepted surgical procedures. Exemplary surgical procedures andassociated surgical instruments are disclosed in the Zimmer SurgicalTechniques, incorporated by reference above. Tibial baseplate 12 isaffixed to tibia T by any suitable method, such as by keel 16 (FIGS. 3A,3C and 4A), adhesive, bone-ingrowth material, and the like.

With tibial baseplate 12 implanted, tibial bearing component 14 may becoupled with tibial baseplate 12 to complete tibial prosthesis 10, suchas by using locking mechanism 26. Once attached, tibial bearingcomponent 14 will leave the posteromedial portion of tibial baseplate 12uncovered to create relief 52 (as shown in FIG. 7 and discussed above).Thus, a surgeon may wish to verify that this anterior-biased,“asymmetrical” orientation of medial articular surface 42 is properprior to permanent affixation of tibial bearing component 14 to tibialbaseplate 12.

To accomplish such verification, tibial bearing component 14 may beplaced side-by-side with trial prosthesis 100, with inferior surface 36of tibial bearing component 14 in contact with superior surface 112 oftrial prosthesis 100. If properly matched with the chosen size andconfiguration of trial prosthesis 100, inferior surface 36 tibialbearing component 14 will substantially cover superior surface 112,leaving only void indicator 106 exposed. Put another way, peripheralwall 54 of tibial bearing component 14 will trace peripheral wall 114 oftibial trial prosthesis 100, excluding the posteromedial area defined byvoid indicator 106. If inferior surface 36 of tibial bearing component14 is a match with superior surface 112 of trial prosthesis 100 exceptfor void indicator 106 (which is left uncovered by tibial bearingcomponent 14), then tibial bearing component 14 is the proper sizecomponent.

When the surgeon is satisfied that tibial bearing component 14 isproperly matched and fitted to the installed tibial baseplate 12,bearing component 14 is secured using locking mechanism 26 and thecorresponding tibial bearing locking mechanism and appropriateinstrumentation (not shown). Exemplary methods for employing lockingmechanism 26 are described in U.S. provisional patent application Ser.Nos. 61/367,374 and 61/367,375 filed Jul. 24, 2010, and U.S. patentapplication Ser. Nos. 13/189,324 and 13/189,328 filed Jul. 22, 2011, allentitled TIBIAL PROSTHESIS, the entire disclosures of which are herebyexpressly incorporated herein by reference.

Bearing component 14 is not movable with respect to baseplate 12 afterthe components have been locked to one another, which is to say theembodiments of prosthesis 10 illustrated herein are “fixed bearing”designs. Thus, proper location and rotational orientation of tibialbearing component 14 upon tibial plate 18 is ensured by cooperationbetween raised perimeter 24 and peripheral recess 46, as well as bylocking mechanism 26 cooperating with central recess 47. Such properorientation results in medial articular surface 42 being generallyanteriorly disposed with respect to medial compartment 22 of tibialplate 18, as noted above. It is also contemplated that the principles ofthe present disclosure may be applied to a “mobile bearing” design inwhich the tibial bearing component is movable in vivo with respect tothe tibial baseplate. In mobile bearing designs, the periphery of thetibial bearing component will generally be smaller than the periphery ofthe tibial baseplate, similar to certain embodiments described above.

Femoral component 60 may be affixed to a distal end of femur F, asappropriate, using any conventional methods and/or components. Exemplarysurgical procedures and instruments for such affixation are disclosed inthe Zimmer Surgical Techniques, incorporated by reference above. Femur Fand tibia T may then be articulated with respect to one another toensure that femur F, femoral component 60 and/or adjacent soft tissuesdo not impinge upon tibial baseplate 12 and/or tibial bearing component14 in deep flexion, such as at a flexion angle β of 155° as shown inFIG. 7. When the surgeon is satisfied with the location, orientation andkinematic profile of tibial prosthesis 10, the knee replacement surgeryis completed in accordance with conventional procedures.

While this invention has been described as having an exemplary design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. (canceled)
 2. A tibial prosthesis comprising: a bearing componentcomprising: a bearing distal surface; an opposing bearing proximalsurface defining a lateral articular surface and a medial articularsurface; and a bearing peripheral wall disposed between the bearingdistal and proximal surfaces; and a baseplate configured to couple tothe bearing component, the baseplate comprising: a baseplate distalsurface configured for contacting a bone surface; an opposing baseplateproximal surface having a medial compartment and a lateral compartment,the bearing component mountable to the tibial baseplate; and a baseplateperipheral wall disposed between the baseplate proximal and distalsurfaces, the baseplate peripheral wall including a baseplatemedial-posterior wall extending distally and posteriorly toward thebaseplate distal surface; wherein the baseplate medial-posterior wallextends in a posterior direction beyond a posterior medial edge of thebearing component such that a posterior most portion of the baseplatemedial-posterior wall does not interface with the bearing component andis exposed when the baseplate is coupled to the bearing component. 3.The tibial prosthesis of claim 2, wherein the baseplate medial-posteriorwall comprises a baseplate chamfer, and wherein the baseplate chamferextends across less than an entirety of a proximal/distal distance ofthe baseplate medial-posterior wall.
 4. The tibial prosthesis of claim2, wherein the baseplate medial-posterior wall comprises a baseplatechamfer, and wherein the baseplate chamfer extends across substantiallyan entirety of a proximal/distal distance of the baseplatemedial-posterior wall.
 5. The tibial prosthesis of claim 2, wherein thebaseplate medial-posterior wall comprises a baseplate chamfer, andwherein the baseplate chamfer defines one of an arcuate profile or alinear profile.
 6. The tibial prosthesis of claim 2, wherein the bearingperipheral wall includes a bearing medial-posterior chamfer extendingdistally and posteriorly from the medial articular surface toward thebearing distal surface.
 7. The tibial prosthesis of claim 6, wherein thebaseplate medial-posterior wall comprises a baseplate chamfer, andwherein the bearing medial-posterior chamfer and the baseplate chamferform one of a substantially continuous or a substantially discontinuouschamfer that extends proximally and anteriorly substantially from aposterior-medial edge of the baseplate to substantially the medialarticular surface.
 8. The tibial prosthesis of claim 2, wherein thebaseplate medial-posterior wall and the bearing peripheral wall at amedial-posterior section are configured to cooperate to create a relieffrom a femur when implanted such that there is a space between the femurand both baseplate medial-posterior wall and the bearing peripheral wallat the medial-posterior section when the femur is in a deep flexionorientation with respect to the tibial prosthesis.
 9. The tibialprosthesis of claim 2, wherein a medial portion of the bearing componentis biased anteriorly relative to a lateral portion such that thebaseplate medial-posterior wall is exposed, and wherein the lateralarticular surface substantially completely covers a lateral compartmentand extends further posterior than the medial articular surface.
 10. Thetibial prosthesis of claim 2, wherein the bearing component comprises arecess formed between the bearing peripheral wall and the bearing distalsurface, and the baseplate includes a projection configured to engagewith the recess when the bearing component is mounted to the tibialbaseplate.
 11. A tibial prosthesis comprising: a bearing componentcomprising: a bearing distal surface; an opposing bearing proximalsurface defining a lateral articular surface and a medial articularsurface; and a bearing peripheral wall disposed between the bearingdistal and proximal surfaces; and a baseplate configured to couple tothe bearing component, the baseplate comprising: a baseplate distalsurface configured for contacting a bone surface; an opposing baseplateproximal surface having a medial compartment and a lateral compartment,the bearing component mountable to the tibial baseplate; and a baseplateperipheral wall disposed between the baseplate proximal and distalsurfaces, the baseplate peripheral wall including a baseplatemedial-posterior wall extending distally and posteriorly toward thebaseplate distal surface; wherein the baseplate medial-posterior wallextends in a posterior direction beyond a posterior medial edge of thebearing component, wherein the baseplate medial-posterior wall and thebearing peripheral wall at a medial-posterior section together extendproximally and anteriorly substantially from a posterior-medial edge ofthe baseplate to substantially the medial articular surface to create arelief from a femur when implanted such that there is a space betweenthe femur and both baseplate medial-posterior wall and the bearingperipheral wall at the medial-posterior section when the femur is in adeep flexion orientation with respect to the tibial prosthesis.
 12. Thetibial prosthesis system of claim 11, wherein a posterior most portionof the baseplate medial-posterior wall does not interface with thebearing component and is exposed when the baseplate is coupled to thebearing component.
 13. The tibial prosthesis of claim 11, wherein thebaseplate medial-posterior wall comprises a baseplate chamfer, andwherein the baseplate chamfer extends across less than an entirety of aproximal/distal distance of the baseplate medial-posterior wall.
 14. Thetibial prosthesis of claim 11, wherein the baseplate medial-posteriorwall comprises a baseplate chamfer, and wherein the baseplate chamferextends across substantially an entirety of a proximal/distal distanceof the baseplate medial-posterior wall.
 15. The tibial prosthesis ofclaim 11, wherein the baseplate medial-posterior wall comprises abaseplate chamfer, and wherein the baseplate chamfer defines one of anarcuate profile or a linear profile.
 16. The tibial prosthesis of claim11, wherein the bearing peripheral wall includes a bearingmedial-posterior chamfer extending distally and posteriorly from themedial articular surface toward the bearing distal surface.
 17. Thetibial prosthesis of claim 16, wherein the baseplate medial-posteriorwall comprises a baseplate chamfer, and wherein the bearingmedial-posterior chamfer and the baseplate chamfer form a substantiallycontinuous chamfer that extends proximally and anteriorly substantiallyfrom the posterior-medial edge of the baseplate to substantially themedial articular surface.
 18. The tibial prosthesis of claim 11, whereina medial portion of the bearing component is biased anteriorly relativeto a lateral portion such that the baseplate medial-posterior wall isexposed, and wherein the lateral articular surface substantiallycompletely covers a lateral compartment and extends further posteriorthan the medial articular surface.
 19. A tibial prosthesis comprising: abearing component comprising: a bearing distal surface; an opposingbearing proximal surface defining a lateral articular surface and amedial articular surface; and a bearing peripheral wall disposed betweenthe bearing distal and proximal surfaces; and a baseplate configured tocouple with the bearing component, the baseplate comprising: a baseplatedistal surface configured for contacting a bone surface; an opposingbaseplate proximal surface having a medial compartment and a lateralcompartment, the bearing component mountable to the tibial baseplate;and a baseplate peripheral wall disposed between the baseplate proximaland distal surfaces, the baseplate peripheral wall including a baseplatemedial-posterior wall extending distally and posteriorly toward thebaseplate distal surface; wherein the baseplate medial-posterior wallextends in a posterior direction beyond a posterior medial edge of thebearing component, wherein a medial portion of the bearing component isbiased anteriorly relative to a lateral portion such that the baseplatemedial-posterior wall is exposed, and wherein the lateral articularsurface substantially completely covers a lateral compartment andextends further posterior than the medial articular surface.
 20. Thetibial prosthesis of claim 19, wherein the baseplate medial-posteriorwall and the bearing peripheral wall at a medial-posterior sectiontogether extend proximally and anteriorly substantially from aposterior-medial edge of the baseplate to substantially the medialarticular surface to create a relief from a femur when implanted suchthat there is a space between the femur and both baseplatemedial-posterior wall and the bearing peripheral wall at themedial-posterior section when the femur is in a deep flexion orientationwith respect to the tibial prosthesis.
 21. The tibial prosthesis ofclaim 19, wherein the baseplate medial-posterior wall comprises abaseplate chamfer, wherein the bearing peripheral wall includes abearing medial-posterior chamfer extending distally and posteriorly fromthe medial articular surface toward the bearing distal surface, andwherein the bearing medial-posterior chamfer and the baseplate chamferform one of a substantially continuous or a discontinuous chamfer thatextends proximally and anteriorly substantially from theposterior-medial edge of the baseplate to substantially the medialarticular surface.